For the purpose of removing phosphorus compounds, e.g., phosphate ions, contained in a wastewater discharged from facilities in the chemical industry, food industry, pharmaceutical industry, fertilizer industry, sewage treatment plants, excreta treatment plants, or the like, the reaction coagulation method is frequently used in which polyvalent ions of a metal such as iron, magnesium, aluminum, or calcium are supplied to the wastewater and reacted with the phosphate ions to thereby convert the phosphate ions into a solid or particles, which is removed by sedimentation, floatation, filtration, etc.
Methods for supplying polyvalent ions of a metal to wastewater include the coagulant addition method in which an aqueous solution of a coagulant such as ferric chloride, poly(ferric sulfate), or poly(aluminum chloride) is supplied with an injection pump (cf. JP-A 2001-48791 (KOKAI)).
Besides such a coagulation method in which a chemical is added, known methods for removing phosphorus compound include the adsorption method in which an ion-exchange resin, hydrotalcite-like clay mineral, zirconium oxide, or the like is used.